Backlighting assembly utilizing microprisms and especially suitable for use with a liquid crystal display

Abstract

An assembly for backlighting a liquid crystal display is disclosed herein along with the liquid crystal display itself and a specific light polarization arrangement. The assembly for backlighting the liquid crystal display includes a backlighting light pipe into which light is directed in a particular manner and a specifically configured arrangement of immediately adjacent microprisms which cooperate with the backlighting light pipe for reflecting light within the ladder upwards through one of its surfaces in a generally collimated manner. The liquid crystal display backlighting assembly is also disclosed including a specifically designed arrangement for collimating the light directed into the light pipe such that the light exiting the light pipe does so on a more collimated manner.

We claim: 
     
       1. An assembly for backlighting a liquid crystal display, comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends;   (b) means for directing light into said light pipe and for causing it to move from one end of the light pipe towards the opposite end thereof; and   (c) an arrangement of immediately adjacent microprisms extending normal to the lengthwise axis of the light pipe from one side of said light pipe to its opposing side along the entire extent of and serving as the bottom surface of the light pipe, each of said microprisms having a triangular cross-section extending downward to a point so as to define from said point opposing, upwardly angled light reflecting surface segments for reflecting light within said light pipe upwards through its top surface in a generally collimated manner.   
     
     
       2. An assembly according to claim 1 wherein all of said microprisms are substantially identical in cross-sectional configuration. 
     
     
       3. An assembly according to claim 1 wherein said microprism arrangement includes a grooved underside, the groove coated with a light opaque, light reflecting coating to enhance reflection. 
     
     
       4. An assembly according to claim 2 wherein each of said microprisms defines an isosceles triangle in cross-section, the equal sides of which in turn define the microprism's opposing light reflecting surface segments. 
     
     
       5. An assembly according to claim 4 wherein each of said microprisms defines an angle of about 100° between its light reflecting surface segments. 
     
     
       6. An assembly according to claim 1 wherein said light pipe is divided into a series of longitudinally extending laterally adjacent light pipe sections which extend from one end of the light pipe to its other end and which are optically isolated from one another along substantially their entire lengths, whereby the individual light pipe sections act on incoming light substantially independently with respect to one another. 
     
     
       7. An assembly according to claim 1 wherein said means for directing light into said light pipe does so from at least one end thereof and includes means for limiting the maximum angle at which light enters the light pipe in relation to the lengthwise axis of the light pipe. 
     
     
       8. An assembly according to claim 7 wherein said microprisms are configured such that the light entering said light pipe and reflected off the angled surface segments of the microprisms is reflected towards the top surface of the light pipe at angles no greater than one-half said maximum angle with respect to lines normal to said top surface. 
     
     
       9. An assembly according to claim 8 wherein said microprisms define substantially identical isosceles triangles, each of which in turn defines an angle of 100° between its light reflecting surface segments and wherein said maximum angle of light entering one light pipe is no greater than 20°. 
     
     
       10. An assembly according to claim 1 wherein said means for directing light into said light pipe does so from at least one end thereof and includes light control means for limiting the maximum angle at which light enters the light pipe in relation to the lengthwise axis of the light pipe. 
     
     
       11. An assembly according to claim 10 wherein said light control means includes a light collimating light pipe having opposing top and bottom surfaces and opposing sides and extends lengthwise between opposite ends, said light collimating light pipe being disposed in end-to-end relationship with and directly adjacent to the light entering end of said back lighting light pipe and being divided into a series of longitudinally extending, laterally adjacent light pipe sections which are optically isolated from one another, each of said light pipe sections having its own opposing top and bottom surfaces and its own opposing sides. 
     
     
       12. An assembly according to claim 11 wherein said means for directing light into said backlighting light pipe includes a single light source extending across and adjacent to the end of said collimating light pipe opposite said backlighting light pipe, whereby light from said light source enters and propagates through each of the divided sections of the collimating light pipe before entering said backlighting light pipe. 
     
     
       13. An assembly according to claim 12 wherein selected ones of the sides and top and bottom surfaces of each of the divided sections of said collimating light pipe include optical coatings which are provided for internally reflecting only that light within the light pipe section which displays incident angles less than a predetermined value, whereby to enhance collimation of the light propagating through each of the divided light pipe sections. 
     
     
       14. An assembly according to claim 13 wherein said maximum angle is no greater than the arcsin n 1  /n 2 , where n 1  and n 2  are refractive indices of said optical coating and the collimating light pipe, respectively. 
     
     
       15. An assembly according to claim 13 wherein said backlighting light pipe is divided into a series of longitudinally extending laterally adjacent light pipe sections which extend from one end of the light pipe to its other end in end-to-end alignment with the divided sections of said collimating light pipe, and which are optically isolated from one another along substantially their entire lengths, whereby the individual light pipe sections act substantially independent with respect to one another. 
     
     
       16. An assembly according to claim 13 wherein said backlighting light pipe is divided into an upper section including its top surface and an optically isolated bottom section including its bottom surface, said light pipe including a series of longitudinally spaced optical coupling strips disposed between said upper and lower light pipe sections and extending from one side of the backlighting light pipe to the opposing side for optically coupling the upper and lower light pipe sections to one another. 
     
     
       17. An assembly according to claim 13 wherein said backlighting pipe is divided into a number of optically isolated layers, said light pipe including a series of longitudinally spaced optical coupling stripe disposed between said layers and extending from one side of the backlighting light pipe to the opposing side for optically coupling the layers to one another. 
     
     
       18. An assembly according to claim 17 wherein at least one of said layers is divided into two optically isolated sections. 
     
     
       19. An assembly according to claim 16 wherein said optical coupling strips progressively widen as a function of distance away from the light entering end of said backlighting light pipe while the spaces therebetween decrease in width. 
     
     
       20. An assembly according to claim 16 wherein said backlighting light pipe includes a Fresnel lens sheet on its top surface and wherein said optical coupling strips are divided in several sections, and such sections use coupling materials of different values of refractive index so that light of different deviation angles can be brought out and distributed systematically along the longitudinal direction of the backlight light pipe and can therefore be corrected by means of said Fresnel lens sheet to achieve a higher degree of collimation. 
     
     
       21. An assembly according to claim 20 wherein said microprisms display systematical changing of angles along the longitudinal direction of the light pipe so that the output light will propagate essentially normal to the surface of the light pipe in the said x-z plane. 
     
     
       22. An assembly according to claim 1 wherein said light pipe is intended to be positioned immediately behind said liquid crystal display so as to receive said generally collimated light, said assembly including a light diffusing light scattering plate member positionable in spaced apart confronting, parallel relationship with the top surface of said light pipe with the liquid crystal display therebetween so that the generally collimated light from said light pipe passes through said liquid crystal display and said plate member, said plate member being configured such that any image appearing thereon as a result of said collimated light does not change appreciably with changes in viewing angles. 
     
     
       23. An assembly according to claim 1 wherein said light entering said light pipe is unpolarized light, said assembly including means for linearly polarizing in a given polarity direction at least approximately half of the light directed out of said light pipe through the top surface thereof. 
     
     
       24. An assembly according to claim 23 wherein said polarizing means includes a polarization arrangement which cooperates with said arrangement of microprisms such that substantially all of the light directed out of said light pipe through the top surface thereof is linearly polarized in said given polarity direction. 
     
     
       25. An assembly according to claim 24 wherein said polarizing means includes a retroreflecting sheet polarizer containing a series of longitudinally extending, adjacent parallel microprisms, said retroreflecting sheet polarizer being positionable in parallel relationship with and in front of the top surface of said light pipe such that said microprisms extend in directions transverse but not perpendicular to the microprisms of said light pipe. 
     
     
       26. An assembly according to claim 25 wherein the microprisms of said retroreflecting sheet polarizer extend in directions which are at 45° angles with the microprisms of said light pipe. 
     
     
       27. An assembly for backlighting a liquid crystal display, comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends, said light pipe being divided into a series of longitudinally extending laterally adjacent light pipe sections which extend from one end of the light pipe to its other end and which are optically isolated from one another along substantially their entire lengths, whereby the individual light pipe sections act substantially independently with respect to one another on incoming light;   (b) means for directing light into said light pipe and for causing it to move from one end of the light pipe towards the opposite end thereof; and   (c) an arrangement of microprisms extending normal to the lengthwise axis of the light pipe from one side of said light pipe to its opposing side along the entire extent of said serving as the bottom surface of the light pipe for reflecting light within said light pipe upwards through its top surface in a generally collimated manner.   
     
     
       28. An assembly according to claim 27 wherein said means for directing light into said light pipe does so from at least one end thereof and includes means for limiting the maximum angle at which light enters the light pipe in relation to the lengthwise axis of the light pipe. 
     
     
       29. An assembly according to claim 28 wherein said microprisms are configured such that the light entering said light pipe and reflected off the angled surface segments of the microprisms is reflected towards the top surface of the light pipe at angles no greater than one-half said maximum angle with respect to lines normal to said top surface. 
     
     
       30. An assembly according to claim 27 wherein said means for directing light into said light pipe does so from at least one end thereof and includes light control means for limiting the maximum angle at which light enters the light pipe in relation to the lengthwise axis of the light pipe. 
     
     
       31. An assembly according to claim 30 wherein said light control means includes a light collimating light pipe having opposing top and bottom surfaces and opposing sides and extends lengthwise between opposite ends, said light collimating light pipe being disposed in end-to-end relationship directly adjacent to the light entering end of said back lighting light pipe and being divided into a series of longitudinally extending, laterally adjacent light pipe sections which are optically isolated from one another, each of said light pipe sections having its own opposing top and bottom surfaces and its own opposing sides. 
     
     
       32. An assembly according to claim 31 wherein said means for directing light into said backlighting light pipe includes a single light source extending across and adjacent to the end of said collimating light pipe opposite said backlighting light pipe, whereby light from said light source enters and propagates through each of the divided sections of the collimating light pipe before entering said backlighting light pipe. 
     
     
       33. An assembly according to claim 32 wherein selected ones of the sides and top and bottom surfaces of each of the divided sections of said collimating light pipe include optical coatings which are provided for internally reflecting only that light within the light pipe section which displays incident angles less than a predetermined value, whereby to enhance collimation of the light propagating through each of the divided light pipe sections. 
     
     
       34. An assembly for backlighting a liquid crystal display, comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends;   (b) an arrangement of microprisms extending normal to the lengthwise axis of the light pipe from one side of said light pipe to its opposing side along the entire extent of and serving as the bottom surface of the light pipe for reflecting light within said light pipe upwards through its top surface in a generally collimated manner; and   (c) means for directing light into said light pipe from at least one end thereof and for causing it to move from one end of the light pipe towards the opposite end thereof, said means for directing light into said light pipe including means for limiting the maximum angle at which light enters the light pipe in relation to the lengthwise axis of the light pipe to an angle no greater than a predetermined angle, said microprisms being configured such that the light entering said light pipe is reflected off the microprisms towards the top surface of the light pipe at angles no greater than one-half said maximum angle with respect to lines normal to said top surface.   
     
     
       35. An assembly for backlighting a liquid crystal display, comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends;   (b) an arrangement of microprisms extending normal to the lengthwise axis of the light pipe from one side of said light pipe to its opposing side along the entire extent of and serving as the bottom surface of the light pipe for reflecting light within said light pipe upwards through its top surface in a generally collimated manner; and   (c) means for directing light into said light pipe from at least one end thereof and for causing it to move from one end of the light pipe towards the opposite end thereof, said means for directing light into said light pipe including light control means for limiting the maximum angle at which light enters the light pipe in relation to the lengthwise axis of the light pipe.   
     
     
       36. An assembly according to claim 35 wherein said light control means includes a light collimating light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends, said light collimating light pipe being disposed in end-to-end relationship directly adjacent to the light entering end of said back lighting light pipe and being divided into a series of longitudinally extending, laterally adjacent light pipe sections which are optically isolated from one another, each of said light pipe sections having its own opposing top and bottom surfaces and its own opposing sides. 
     
     
       37. An assembly for providing backlighting comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends;   (b) means for directing light into said light pipe and for causing it to move from one end of the light pipe towards the opposite end thereof; and   (c) an arrangement of immediately adjacent microprisms extending normal to the lengthwise axis of the light pipe from one side of said light pipe to its opposing side along the entire extent of and serving as the bottom surface of the light pipe, each of said microprisms having a triangular cross-section extending downward to a point so as to define from said point opposing, upwardly angled light reflecting surface segments for reflecting light within said light pipe upwards through its top surface in a generally collimated manner.   
     
     
       38. An assembly for providing backlighting comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends, said light pipe being divided into a series of longitudinally extending laterally adjacent light pipe sections which extend from one end of the light pipe to its other end and which are optically isolated from one another along substantially their entire lengths, whereby the individual light pipe sections act substantially independently with respect to one another on incoming light;   (b) means for directing light into said light pipe and for causing it to move from one end of the light pipe towards the opposite end thereof; and   (c) an arrangement of microprisms extending normal to the lengthwise axis of the light pipe from one side of said light pipe to its opposing side along the entire extent of said serving as the bottom surface of the light pipe for reflecting light within said light pipe upwards through its top surface in a generally collimated manner.   
     
     
       39. A liquid crystal display assembly, comprising: (a) a backlighting light pipe having opposing top and bottom surfaces and opposing sides and extending lengthwise between opposite ends;   (b) means for directing unpolarized light into said light pipe and for causing it to move from one end of the light pipe towards the opposite end thereof;   (c) an arrangement of immediately adjacent microprisms serving as the bottom surface of the light pipe for reflecting light within said light pipe upwards through its top surface in a generally collimated manner;   (d) means for linearly polarizing in a given polarity direction the light directed out of said light pipe through the top surface thereof, said polarizing means including a polarization arrangement which cooperates with said arrangement of microprisms such that substantially all of the light directed out of said light pipe through the top surface thereof is linearly polarized in said given polarity direction, said polarizing means including a retroreflecting sheet polarizer containing a series of longitudinally extending, adjacent parallel microprisms, said retroreflecting sheet polarizer being positionable in parallel relationship with and in front of the top surface of said light pipe such that said microprisms extend in directions transverse but not perpendicular to the microprisms of said light pipe.   
     
     
       40. An assembly according to claim 39 wherein the microprisms of said retroreflecting sheet polarizer extend in directions which are at 45° angles with the microprisms of said light pipe.